The Moon

The Moon is the only
natural satellite of the
Earth, and the
fifth largest satellite in the
Solar System. It is the largest natural
satellite of a planet in the Solar System relative to the size of its
primary, having a quarter the diameter of Earth and 1⁄81 its
mass. The Moon is the
second densest satellite after Io, a satellite of Jupiter. It is in
synchronous rotation with Earth, always
showing the same face; the
near side is marked with dark volcanic
maria among the
bright ancient crustal highlands and prominent
impact craters. It is the brightest
object in the sky after the Sun,
although its surface is actually very dark, with a similar reflectance to coal.
Its prominence in the sky and its regular cycle of phases have,
since ancient times, made the Moon an important cultural influence on
language, calendars,
art and
mythology. The Moon's gravitational
influence produces the ocean tides and
the minute lengthening of the day. The
Moon's current orbital distance, about thirty times the diameter of the Earth,
causes it to appear almost the same size in the sky as the Sun, allowing it to
cover the Sun nearly precisely in total
solar eclipses.

After the Apollo 17 mission in 1972, the Moon has
been visited only by unmanned spacecraft, notably by the final
SovietLunokhodrover. Since 2004, Japan, China, India,
the United States, and the
European Space Agency have each sent
lunar orbiters. These spacecraft have contributed to confirming the discovery of
lunar water ice in permanently shadowed
craters at the poles and bound into the lunar
regolith. Future
manned missions to the Moon have been planned, including government as well as
privately funded efforts. The Moon remains, under the
Outer Space Treaty, free to all nations
to explore for peaceful purposes.

Mare Crisium (the "sea of crises") is a
lunar mare located in the Moon's Crisium
basin, just northeast of
Mare Tranquillitatis. This basin is of the
Nectarianepoch, while the mare material is of the
Upper Imbrianepoch. This mare is 376 miles
(605 KM) in diameter, with many notable features in and around it.